1. Field of the Invention
The present invention relates to a sol which particles containing cerium oxide as a main component and lanthanum compounds or neodymium compounds are dispersed into a medium, and a process for producing of the sol. The particles containing cerium oxide as a main component and lanthanum or neodymium as other component can be used as abrasives, ultraviolet absorbing materials, catalyst materials, fuel cell materials and the like.
2. Description of the Related Art
Japanese Patent Laid-open No. Sho 56-131686 discloses a cerium oxide powder containing lanthanum wherein the powder is produced by mixing simultaneously cerium salt, a basic solution and a solution of salt in which an anion can form an insoluble rare earth oxide, the resulting precipitate is filtered out, drying it at a temperature of 100 to 600° C., calcinating at a temperature of 600 to 1200° C., and pulverizing the calcined material.
Japanese Patent Laid-open No. Hei 10-95614 discloses a process for producing crystalline cerium oxide powders having a particle size of 0.005 to 5 μm in which the process comprises reacting a cerium (III) salt with an alkaline substance in (OH−)/(Ce3+) molar ratio of 3 to 30 to form a suspension of cerium (III) hydroxide, and immediately blowing oxygen or a gas containing oxygen into the suspension under atmospheric pressure at a temperature of 10 to 95° C.
Japanese Patent Publication No. Sho 63-27389 discloses a polishing composition comprising 40 to 99.5 wt % of ceric oxide and 0.5 to 60 wt % of at least one colorless oxide of other rare earth element selected from the group consisting of lanthanide and yttrium.
Japanese Patent Publication No. Sho 60-35393 discloses a polishing composition of cerium system corresponding to the following formula: Ln2-xCexSi2O7 wherein Ln is at least one element selected from the group consisting of lanthanoid and yttrium and x is a number of not less than 0 and less than 2.
The process for producing ceric oxide powders comprising drying, calcination and pulverization in which the powders contain lanthanum or neodymium, gives powders having uneven particle size and merely gives powders of submicron order at most because the pulverization is employed in order to finely divide particles.